Magnetic sensors having a large magnetoresistive ratio and thermal stability, frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors, are used for a number of sensor applications. Examples of these applications include recording heads, magnetic random access memory, switches, and various sensors that rely on a change in resistance to produce a signal.
A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-magnetic spacer layer. One of the ferromagnetic layers is called the xe2x80x9cpinned layerxe2x80x9d because it is magnetically pinned or oriented in a fixed direction by an adjacent antiferromagnetic layer, commonly referred to as the xe2x80x9cpinning layer,xe2x80x9d through exchange coupling. The other ferromagnetic layer is called the xe2x80x9cfreexe2x80x9d or xe2x80x9cunpinnedxe2x80x9d layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields. In a spin valve sensor, a change in resistance of a layered magnetic sensor is used to read data from a magnetic medium. This change is attributed to spin dependent transport of conduction electrons between the free magnetic layer and one or more pinned magnetic layers through the non-magnetic spacer layers.
Spin valve sensors benefit from the change of resistance exhibited by the devices, which can depend on the relative alignment between the magnetization of the two ferromagnetic layers. In many practical spin valve GMR heads, the layers have scattering at the boundaries that can limit the size of the GMR. This occurs when the thickness of the layers is comparable with or smaller than the mean free path of the conduction electrons. The scattering of conduction electrons depends on an interaction between the spin polarization and the magnetic orientation of the free and pinned layers. The more interfaces the electron goes through without being scattered, the larger the GMR value. In the existing spin valve applications, most of the electrons are scattered after entering the metallic capping layers or antiferromagnetic layer and no longer contribute to the GMR effect.
Synthetic antiferromagnetic (xe2x80x9cSAFxe2x80x9d) spin valve structures have also been produced. SAF spin valve structures can provide higher magnetic and thermal stability than simple spin valve structures. A SAF spin valve includes a pinned layer structure that is composed of two ferromagnetic layers, separated by a nonmagnetic spacer layer. The first magnetic layer is called the pinned layer. The non magnetic layer is called the antiferromagnetic (xe2x80x9cAFMxe2x80x9d) coupling layer. The second magnetic layer is called the reference layer. Similar to the layers of a simple spin valve, a SAF spin valve replaces the pinned layer of the simple spin valve with the layers of the SAF structure.
Specular reflection has been obtained using insulators as capping layers and antiferromagnetic pinning layers. This enhancement to the GMR has been demonstrated in Co/Cu based spin valves with NiO as the antiferromagnetic pinning layers. These spin valves, however, may have disadvantages when used for GMR head applications due to their poor thermal stability. The improvement of magnetoresistive ratios can also improve device sensitivity and enable new applications. This invention discusses some of these concerns.
Accordingly, the present invention relates to a spin valve structure encompassing specular reflection layers to improve the magnetoresistive ratio and sensitivity of the spin valve.
In one aspect of this invention, a spin valve structure is presented. The spin valve structure includes a first ferromagnetic layer separated from a second ferromagnetic layer by a non-magnetic layer. The spin valve structure also includes a first specular scattering layer separated from a second specular scattering layer by the first ferromagnetic layer, the non-magnetic layer, and the second ferromagnetic layer. The first ferromagnetic layer can include a free layer and the non-magnetic layer can include a spacer layer. The second ferromagnetic layer can include a pinned layer or a reference layer. The specular scattering layers can include a material such as Y2O3, HfO2, MgO, Al2O3, NiO, Fe2O3, and Fe3O4.
The spin valve structure can include an antiferromagnetic layer separated from the second ferromagnetic layer by the second specular scattering layer. Additionally, the spin valve structure can include a seed layer separated from the second specular scattering layer by the antiferromagnetic layer. The seed layer can also be separated from the first ferromagnetic layer by the first specular scattering layer.
In another aspect of the invention, the spin valve structure, the second specular scattering layer can be separated from the antiferromagnetic layer by a second pinned layer. The second specular scattering layer can be separated from the antiferromagnetic layer by an antiferromagnetic coupling layer, the antiferromagnetic coupling layer can be separated from the antiferromagnetic layer by a pinned layer, and the second ferromagnetic layer can include a reference layer. Additionally, the second specular scattering layer is separated from the antiferromagnetic coupling layer by a second reference layer. The antiferromagnetic coupling material can include a material such as Ru, Rh, and Cr.
The spin valve structure can also include a pinned layer separated from the second ferromagnetic layer by the second specular scattering layer. The second specular scattering layer can include a mixture of a specular scattering material and an antiferromagnetic coupling material. The specular scattering material comprises can include a material such as Y2O3, HfO2, MgO, Al2O3, NiO, Fe2O3, and Fe3O4, and the antiferromagnetic coupling material can include a material such as Ru, Rh, and Cr. In the spin valve structure, the first and second ferromagnetic layer can include Co and Fe.
In another aspect of this invention, a method for forming a spin valve structure is presented. The method includes depositing a first ferromagnetic layer separated from a deposited second ferromagnetic layer by a deposited non-magnetic layer. A first specular scattering layer separated from a deposited second specular scattering layer by the first ferromagnetic layer, the non-magnetic layer, and the second ferromagnetic layer is also deposited.
The method can also include depositing a pinned layer separated from the second ferromagnetic layer by the second specular scattering layer, when the second ferromagnetic layer includes a deposited reference layer, and the deposition of the second specular scattering layer includes co-depositing a mixture of a specular scattering material and an antiferromagnetic coupling material.
The details of the methodology can be found in the Detailed Description section below. The advantages of this invention may include the following. The use of the two specular scattering layers can increase the GMR sensitivity of the spin valve structure. The specular scattering layers can also be placed within a SAF structure, which can enhance the GMR and maintain the strong coupling.